1. Field of the Invention
The present invention relates generally to a mobile communication system, and more particularly, to a method and system for managing an inactive interval of a Base Station (BS) to minimize power consumption of the BS.
2. Description of the Related Art
Along with increased global attention on energy saving as a solution to environmental problems, the concept of green Information Technology (IT) has been introduced to the IT industry and many techniques for energy conservation have been developed. In this context, each mobile communication system has introduced the concept of a sleep mode to reduce power consumption of a pico/femto BS installed in a small space such as a building. For example, the Institute of Electrical and Electronics (IEEE) 802.16m standard defines a sleep mode called a “low-duty mode” for a BS.
Upon entering the low-duty mode, a BS activates an air interface and performs normal functions such as paging, broadcast message transmission, ranging, and traffic transmission during an available interval, whereas the BS inactivates the air interface during an unavailable interval. Therefore, the power consumption of the BS is reduced and interference with neighbor BSs is reduced during the unavailable interval.
To reduce power consumption and interference, an available interval and an unavailable interval are defined for a BS in each mobile communication system. Inactivation of a Radio Frequency (RF) interval during an unavailable interval is currently under consideration. For this purpose, a Low-Duty Mode (LDM) operation is performed, as will be described below, according to IEEE 802.16m.
A BS determines an LDM pattern for use during its available and unavailable intervals. The LDM pattern specifies an available interval, an available interval, and a start superframe number. An operation of the BS to be performed may be predicted from the LDM pattern. If all User Equipments (UEs) connected to a BS are in a sleep state or an idle state, the BS may enter the LDM. The BS transmits a message carrying an LDM pattern to the UEs. The UEs determine an operation pattern of the BS according to the LDM pattern and operate in accordance with the LDM operation of the BS.
When the BS autonomously determines its LDM pattern, its power conservation is optimized. However, if an available interval of the BS coincides with an available interval of a neighbor BS, mutual interference may occur between the BSs.
FIG. 1 illustrates a scenario in which two adjacent BSs enter their available intervals at the same time, creating interference at a cell edge.
Referring to FIG. 1, a first UE 130 (UE1) is connected to a first BS 110 (BS1), a second UE 140 (UE2) is connected to a second BS 120 (BS2), and the first UE 130 and the second UE 140 are located at a cell boundary between the first BS 110 and the second BS 120. As available intervals of the first BS 110 and the second BS 120 coincide, mutual interference occurs.
Accordingly, a need exists for a technique for preventing a BS using an LDM from interfering with a neighbor BS.